Conventional power converter control circuits and methods have been driven towards more precise control of output voltage and current. Achieving better precision, such as by pulse width modulation (PWM) is crucial for many power converter applications, allowing conventional switched mode power converter to be used in applications where previously only linear regulation was acceptable for control of output parameters.
However, not all applications require high degrees of precision, or high speed feedback controlled power converters. For example, in providing charge current to a battery, precise control of the charge current level is not necessary. Most types of rechargeable batteries will accept charge (unless they are already fully charged) in proportion to the charge current, and wide variations in the charge current will not harm the battery. The average current is a more important parameter than the precise level of the charge current in most cases.
Many battery charging systems currently marketed, particularly those for use with portable communications and computing equipment, utilize a microcontroller or microprocessor, in conjunction with suitable instruction code, to carry out charging regimes. Many of these same charging systems utilize PWM controlled power converters to control the charge current level, under control of the microprocessor. Typically a PWM controller integrated circuit (IC) is used, such as a TL494, which is manufactured by Motorola, Inc., among many others. However, one of the market drivers for battery chargers in consumer markets is cost. Incorporating the function of the PWM controller IC into the microprocessor would seem an ideal solution. Unfortunately, because of the speed at which a PWM control IC operates in order to effectively control power converter output parameters, the cost of a microprocessor fast enough to carry out PWM control would likely be more than the benefit of integration. Therefore, there exists a need for simple, low cost, digitally operated power converter control circuit that may be integrated with an inexpensive microprocessor.